Not much will be changing here as lists are currently and will continue to be provided by the underlying text engine (what you see in TextEdit). The documentation doesn’t cover much of this stuff in depth for that reason, and instead points you to the TextEdit help if you need details on how to use the Mac text system.
That said, you can start a list with any arbitrary number using the “Other…” option at the bottom of the list type selection menu. Since this panel is for making custom list types overall, it is therefore easier to make your list using the prebuilt type you prefer (like “a) b) c)”) and then use the custom list tool to change the starting point for the current list, as doing things in that order will pre-fill the customisation options for making a list that looks that way, rather than having to start from scratch.